1. Field of the Invention
This invention relates to tires and more particularly to non-pneumatic tires that preferably are suitable for off-the-road vehicles. The non-pneumatic tires have multiple radial regions of differing hardness and preferably an outer radial region that is harder than an inner radial region.
2. Discussion of the Background Information
Off-the-road (OTR) vehicles, also known as off-highway vehicles, are commonly used in rugged terrain for mining, excavation, construction, military applications, and other heavy industrial applications. OTR vehicles include tractors, trucks, loaders, dozers, graters, excavators, etc., and may have operational weights as high as 380 to 460 tons. Typically such OTR vehicles have several inflatable tires made of rubber. These applications require that each tire have properties such as being puncture-proof, able to carry relatively heavy loads, and good resistance to wear and tear. Conventional inflatable tires generally have short operational life spans of about six months. Further, the typical rugged operating environment for OTR vehicles exposes the tires to possible failures, such as punctures, blowouts, tears, and separation of the tire from the rim. Thus, the time and cost to maintain such OTR vehicles increases because the inflatable tires need to be replaced due to normal wear and tire failure. For mining vehicles, for example, shortages of suitable replacement tires may cause a mine operator to shut down production while waiting for new replacement tires. This may cause particular hardships for remotely located mines that receive sporadic or irregular shipments of new supplies.
While improvements in the durability of such inflatable tires continue to be made, such tires are still exposed to normal wear and failure. Thus, the need exists for tires suitable for OTR vehicles that overcome the shortcomings of conventional inflatable tires.
One solution is to use a solid non-pneumatic tire. Urethane elastomers have been used in the manufacture of solid tires for such applications as industrial tires, off-the-road tires, bicycles tires, etc. Urethane solid tires, however, have not been entirely satisfactory in such applications because they do not have desirable cushioning and handling characteristics. Also, such solid tires suffer from internal heat build-up and subsequent degradation of the elastomer material in prolonged high speed service conditions or under rough terrain situations where the tire is being deformed. Various non-pneumatic tire designs have been proposed to overcome these limitations of pneumatic tires and solid non-pneumatic tires.
Some designs of non-pneumatic tires have cavities formed into the sidewall, such as those described in International Publications WO2008/009042 and WO97/18959, U.S. Publication No. 2007/0215259, U.S. Pat. Nos. 7,174,936, 5,676,900, 5,343,916, 5,223,599, 5,139,066, 5,023,040, 4,921,029, 4,784,201, and EP Publication 0399383, the entire contents and disclosures of which are hereby incorporated by reference. Metal bands are often used as a reinforcement means to provide support in these non-pneumatic tire designs. Also, some of the non-pneumatic tires incorporate a separate rubber tread.
Some designs of non-pneumatic tires have resilient members that create openings laterally through the sidewall, such as those described in U.S. Publication No. 2007/0089820 and U.S. Pat. Nos. 7,201,194, 7,013,939, 6,681,822, 6,170,544, 4,945,962, 4,226,273, and 3,219,090, and EP Publication 0353006, the entire contents and disclosures of which are hereby incorporated by reference.
Various tire ornamental designs for pneumatic and non-pneumatic tires, including industrial tires, have also been proposed, such as those shown in U.S. Design Pat. No. D201,238, D329,413, D401,896, D410,603, D455,996, D498,203, D499,065, D536,298, and D548,681, the entire contents and disclosures of which are hereby incorporated by reference.
However, there is still a need for improved non-pneumatic tires, particularly for use in large off-the-road vehicles.